About AXI2021-02-26T07:53:39+00:00

About AXI

True 3D X-ray inspection was another Saki first!

Automated X-ray inspection, or AXI, is a technology that uses X-rays to examine the features of a printed circuit board, semiconductor package, or power module that are hidden from view and therefore cannot be captured by automated optical inspection (AOI), which uses visible light as its source.

True 3D X-ray inspection is another Saki first. Most so-called “3D” X-ray systems have really been 2.5D because they work on the basis of deconstruction, where they capture an image and have to remove the images from the underside of the board. Saki’s system works on the basis of reconstruction. Saki’s very high resolution planar computed tomography (PCT) technology is an extension of CT scanners used in the medical field and was developed in-house by Saki engineers and scientists. The automated inspection process completely separates the top and bottom-side images of the board so images are not affected by back-side mounting. Saki’s PCT technology utilizes a high-resolution image composed from 200 imaging slices acquired through the board, solder joints, and components, whereas other AXI machines only use about five slices for imaging.

Saki’s AXI systems address 3 market segments:

Printed circuit board (PCB) – usually part of the PCB assembly process after reflow:

  • Solder ball joint inspection of BGAs
  • Solder joint inspection on the back face of QFNs
  • Solder joint inspection for all parts such as chips, connectors, and insert parts on the PCB

Power module:

  • High power X-ray tubes (225kV)
  • Void inspection inside the solder joint of an insulated gate bipolar transistor (IGBT) module


  • High resolution inspection (defect inspection down to 15μm)
  • Void inspection of laser through-holes (LTH)
  • Flip chip bonding inspection
  • Package-on-package (PoP) soldering inspection

AXI is the best technology for accurately reconstructing the shape of solder balls and fillets to perform reliable solder inspection.

Saki’s AXI systems don’t just inspect, they combine the layers, measure components and features, determine placement variance and warpage, and analyze their internal structures for a true volumetric representation of continuous 3D images without joints. Saki’s BF-X3 system offers a programmable resolution from 13–30 microns. Reconstruction of images is done on-the-fly, for every solder joint, creating 3D data for the entire sample. Defects are identified and classified, including 100% of head-in-pillow defects, voids, and dry joints. This results in best-in-class Cpk and gage repeatability and reproducibility, which is particularly critical in aerospace, medical, automotive, and other applications where failure is not an option.

High-resolution 3D data is used for all image acquisition, inspection, and analysis. A high-resolution image of each defect is displayed immediately, thereby enabling prompt viewing and analysis and eliminating the need for further analytical equipment. Such precision machine control, 3D reconstruction, 3D inspection, and 3D viewing are all unique developments by Saki.

AXI inspects for:

  • Absence of solder
  • Bridging
  • Dry joints
  • Fillet defects
  • Foreign material
  • Head-in-pillow and non-wetted defects
  • Insufficient solder
  • Lifted bump
  • Lifted chips
  • Lifted leads
  • Misalignment
  • Opens
  • Presence or absence of components
  • Shorts
  • Tombstones
  • Voids

Components and packages that are usually inspected are:

  • Aluminum electrolytic capacitors
  • Ball grid arrays (BGAs)
  • Chip scale packages (CSPs)
  • Chip type parts
  • Connectors
  • Diodes
  • Land grid array (LGA)
  • Module chips
  • Power transistors
  • Quad flat no-leads (QFN)
  • Quad flat packs (QFPs)
  • Small outline packages (SOPs)
  • Tantalum Capacitors
  • Transistors

Saki’s 3D inline AXI product line consists of the:

  • BF-X2 225kV system for semiconductor and power module inspection
  • BF-X2 160kV in-line 3D automated X-ray inspection system for high power resolution
  • BF-X3 system for printed circuit board assembly

Saki’s AXI systems meet the highest safety standards

Saki’s BF-X3 AXI system keep X-ray emissions at a stable and safe level and are able to start inspection quickly, due to the three shutters located at the PCB entrance, PCB exit, and X-ray emission site. These shutters allow quick inspection by eliminating the need to turn off the X-ray source during board transfer in and transfer out of the machine. The X-ray leakage dose is less than 0.5 μSv/h, thereby allowing an operator to work 40 hours per week/2,000 hours per year,* safely and securely. The system meets rigid European (CE) standards.

* The time is calculated according to dosage constraints in public exposure (1 mSv per year) indicated in the 2007 recommendations of the ICRP.